Electronic components, such as portable computers and handheld electronic devices, are becoming increasingly popular and are often provided with wireless communications capabilities. For example, electronic components may use long-range wireless communications circuitry to communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands). Electronic components may also use short-range wireless communications links to handle communications with nearby equipment. For example, electronic components may communicate using the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz (sometimes referred to as local area network bands) and the Bluetooth® band at 2.4 GHz. To form the antenna structure of such electronic components, molded interconnect devices (“MID”) often contain a plastic substrate on which is formed conductive elements or pathways. Such MID devices are thus three-dimensional molded parts having an integrated printed conductor or circuit layout, which saves space for use in smaller devices (e.g., cellular phones). It is becoming increasingly popular to form MIDs using a laser direct structuring (“LDS”) process during which a computer-controlled laser beam travels over the plastic substrate to activate its surface at locations where the conductive path is to be situated. With a laser direct structuring process, it is possible to obtain conductive element widths and spacings of 150 microns or less. As a result, MIDs formed from this process save space and weight in the end-use applications. Another advantage of laser direct structuring is its flexibility. If the design of the circuit is changed, it is simply a matter of reprogramming the computer that controls the laser. This greatly reduces the time and cost from prototyping to producing a final commercial product.
Various materials have been proposed for forming the plastic substrate of a laser direct structured-MID device. For example, one such material is a blend of polycarbonate, acrylonitrile butadiene styrene (“ABS”), copper chromium oxide spinel, and a bisphenol A diphenyl phosphate (“BPADP”) flame retardant. One problem with such materials, however, is that the flame retardant tends to adversely impact the mechanical properties (e.g., deformation temperature under load) of the composition, which makes it difficult to use in laser direct structuring processes. Such materials are also unsuitable for lead free soldering processes (surface mount technology) that require high temperature resistance. Another problem is that the materials tend to have a low dielectric constant, which makes it difficult to use them in applications where it is desired to include more than one antenna in the device. To this end, various high dielectric materials have been proposed. For instance, one material that has been proposed includes a blend of polyphenylene oxide, nylon, or polyamide with barium titanate and copper chromium oxide spinel. Unfortunately, with these materials, high loadings of barium titanate are generally required to achieve the desired dielectric constant, which has an adverse impact on mechanical properties and pressure required to fill a thin walled part in injection molding. In addition, many flame retardants tend to corrode the mold and screw used in injection molding.
As such, a need exists for a thermoplastic composition that can be activated by laser direct structuring and has a relatively high dielectric constant, but still maintain excellent mechanical properties and processibility (e.g., low viscosity).